rockyou, apologies for not getting back to you on your question. the days that this showed up for me have been only hot days and 75+ mile drives. After a good couple of long hours of sitting in a cool garage, the car would act normal again... After changing out the relay, i have been in several hotdays and long drives with no problem.

BTW, I have seen other cars (including CIS p-cars)run with the 02 sensor unplugged and on the dyno, they have shown to have A/F ratios that were all over the place and making lousy power. I wouldn't rule out the 02 relay being the culprit just because the 02 sensor was not hooked up by the PO; the relay and the lambda brain both play important parts in the CSI system. If all the hardware is there, why not try to hook it up and get the car running as it was designed? Just a thought buddy.

Same symptoms as you describe. The relay is $15, I think. If your lucky it will be a cheap fix.

Good luck

I've actually found one of the spark plug connector to have relative more resistance then the other ones, with 20k ohm... the other ones have 2.5 to 3k ohm... not sure if that would make such a big different though...

rockyou pm'd me, because I did indeed forget to post my results, but I finally remembered :) No change. It was a cool rainy day, so I wasn't driving as hard as usual, but by the end of the day I was still having the hesitation issue. I pitted to let the car cool, and after as little as 5 minutes I noticed an improvement, so it's definitely a heat thing. I guess next is to replace the coil?

ok, $0.02 from a fellow CIS owner here. Read Souk's CIS thread. Read it again if you don't understand it. Then the following will make sense:

1. Adjust your valves. Not your problem here, but do it anyway. No point troubleshooting if you know there is a problem elsewhere

2. Check your clock. Does it work? If not, replace your fuse in the front block, enjoy the light from your dome lamp and go for a drive. If you have time and light, your car should run much better. This circuit is the power to the lambda. Porsche chose a weird way to wire things, but c'est la vie.

3. With the engine idling, take off the air filter and lift up on the right flapper. Does the engine speed up or die? This tells you if you are even in the right a/f ballpark.

4. Reconnect the 02 sensor. That is a "fix" for the weak. Make sure everything else is right rather than masking the problem with a full rich condition.

I think you have a mixture problem. Not necessarily the initial setting, but how the system reacts with rpm, temperature, etc affects driveability. Remember, CIS sets a/f with pressure and this is constantly varying. A bad mixture set will also create a hot start problem.

Oh, and CIS has many pieces that change and adjust this mixture so make sure that they are all roughly working. See point #1. Then fine tune.

Good luck!

I've played around with the mixture a bit, and it seems to have solved the problem, although other mixture symptoms came out. So to be sure I've finally asked a Porsche mechanic to tune it for me, and it runs fine now! :)
However I still have to leave my O2 sensor disconnected, 'cause when it's connected the revs became unstable when idle and in low rpm driving. By reading some old threads, someone has suggested that it may be the air flow meter? However it seems hard to find information about how to test or tune this thing...